Physical Properties of Minerals

Dr. Ahmad Redaa

2024-09-16

Physical Properties of Minerals

Minerals exhibit a range of physical properties that help in their identification.
Properties are linked to their internal structure and chemical composition.
In this lecture, the following properties will be covered:
- Mineral Appearance ( Luster- transparency- Color - Streak – Luminescence - Play of Colors)
- Strength and Breaking (Tenacity - Cleavage, Fracture, and Parting – Hardness -
- Density and Specific Gravity
- Magnetism
- Electrical Properties
- Reaction to Dilute Hydrochloric Acid

Mineral Appearance: Luster

Luster refers to the way light interacts with the surface of a mineral.
Types: Metallic, Submetallic, Non-metallic (e.g., vitreous, pearly, silky)
Luster can be seen by observing the mineral’s surface under normal light.

Source: https://slideplayer.com

Mineral Appearance: Transparency (diaphaneity)

Transparency refers to how much light passes through the mineral.
Types: Transparent, Translucent, Opaque

Source: https://slideplayer.com

Mineral Appearance: Color

Color is the visible hue of a mineral but can vary due to impurities.
How to Describe: Observe the mineral’s color in natural light.

Examples of the colours of the minerals sulphur and hematite., Source: Earle, S. (2019)

Mineral Appearance: Streak

Streak is the color of the mineral’s powder when rubbed on a streak plate.
How to examine: Use an unglazed porcelain plate to observe the powder color.

Source: Earle, S. (2019)

Mineral Appearance: Luminescence

Luminescence is the emission of light by a mineral when exposed to UV light.
Example: Fluorite glows under UV light.

Minerals under normal light (top) and their luminescent response under UV light (bottom), Source: https://www.earthsciences.hku.hk

Mineral Appearance: Play of Colors

Play of colors refers to iridescence or changing colors when viewed from different angles.
How to examine: Move the mineral to observe changes in color.
Example: Labradorite exhibits play of colors.

Strength and Breaking: Tenacity

Tenacity describes a mineral’s resistance to breaking, bending, or deforming.
Types: Brittle, Malleable, Ductile, Flexible
Example: Gold (malleable), Sulfur (brittle)

Strength and Breaking: Cleavage and Fracture

Cleavage is the property of a mineral that allows it to break smoothly along specific internal planes (called cleavage planes)
fracture is the property of a mineral breaking in a more or less random pattern with no smooth planar surfaces.
Example: Mica (perfect cleavage), Quartz (conchoidal fracture)

Source: Earle, S. (2019)

Strength and Breaking: Hardness

Hardness refers to a mineral’s resistance to scratching.
Mohs Hardness Scale (1-10)
How to Examine: Scratch the mineral with a reference material (nail or coin) and observe what scratches it.

Source: https://www.nps.gov

Density and Specific Gravity

Density is the mass per unit volume
Specific gravity is the ratio of a mineral’s density compared to water.
Example: Galena (high specific gravity), Quartz (low specific gravity)

Source: https://byjus.com

Magnetism

Definition: Magnetism refers to a mineral’s ability to attract or be affected by a magnet.
How to examine: Test the mineral’s response with a magnet.
Example: Magnetite (strongly magnetic), Hematite (weakly magnetic)

Reaction to Dilute Hydrochloric Acid

Definition: Some minerals react by fizzing or bubbling when exposed to dilute hydrochloric acid. - How to Examine: Apply a drop of acid and observe for fizzing. - Example: Calcite (reacts strongly), Dolomite (reacts weakly)